1. Field of the Invention
The present invention relates generally to the testing of medical electrodes that are mounted on a release liner. More particularly, the invention is directed to various electrode and/or release liner embodiments that facilitate testing and characterization of packaged electrodes.
2. Description of the Background Art
Sudden Cardiac Arrest (SCA) is one of the leading causes of death in the industrialized world. SCA typically results from an arrhythmia condition known as Ventricular Fibrillation (VF), during which a patient's heart muscle exhibits extremely rapid, uncoordinated contractions that render the heart incapable of circulating blood. Statistically, after four minutes have elapsed, the patient's chance of survival decreases by 10% during each subsequent minute they fail to receive treatment.
An effective treatment for VF is electrical defibrillation, in which a defibrillator delivers an electrical pulse, waveform, or shock to the patient's heart. Because the onset of VF is generally an unpredictable event, the likelihood that a victim will survive increases dramatically if 1) defibrillation equipment is nearby; 2) such equipment is in proper working order; and 3) such equipment may be easily, rapidly, and effectively deployed to treat the patient.
Medical equipment manufacturers have developed Automated External Defibrillators (AEDs) that minimally trained personnel may use to perform electrical defibrillation when emergency situations arise. AEDs may be found in a variety of non-medical settings, including residences, public buildings, businesses, private vehicles, public transportation vehicles, and airplanes.
An AED relies upon a set of electrodes to deliver a series of shocks to a patient. An electrode therefore serves as a physical and electrical interface between the AED and the patient's body. In general, an electrode may comprise a conductive foil layer that resides upon a conductive adhesive layer; a lead wire that couples the foil layer to the AED; and an insulating layer that covers the foil layer. The conductive adhesive layer physically and electrically interfaces the foil layer to a patient's skin. New or unused electrodes reside upon a release liner, from which an operator may peel off an electrode prior to placement upon a patient's body. During manufacture, electrodes upon their release liner are typically sealed in a package.
An AED is likely to be used infrequently; however, any given use may involve a time critical, life threatening situation. Thus, it is imperative that the AED be able to provide an indication of its operating condition at essentially any time. While in a quiescent state, an AED generally performs periodic diagnostic sequences to determine its current operating condition. Such sequences may be performed, for example, on a daily and/or weekly basis. The diagnostic sequences include tests for characterizing the current path between the AED and a set of electrodes. Hence, the electrodes must be connected to the AED while the AED is in its quiescent state, and the electrodes must be electrically testable while mounted on their release liner. As a result, release liners providing electrical contact between electrodes have been developed.
Such release liners generally include multiple openings that facilitate electrical contact between electrodes. The current path between the AED and the electrodes includes each electrode's lead wire, foil layer, and conductive adhesive layer. For a pair of new, properly functioning conventional electrodes mounted upon a release liner having multiple openings, this current path may be characterized by an impedance value ranging between 2 and 10 Ohms. If an impedance measurement indicates an electrical discontinuity or open circuit condition exists, a lead wire or connector coupling an electrode to the AED may be damaged, and/or an electrode may be improperly connected to the AED. Similarly, if an impedance measurement indicates a short or open circuit condition exists, one or more electrodes, a lead wire or other wire within the current path, and/or a connector that couples the electrodes to the AED may be damaged or defective.
A measurement indicating a higher than desired impedance may arise when an electrode is damaged, deteriorated, and/or degraded. An electrode's conductive adhesive layer typically comprises a hydrogel film, which itself comprises natural and/or synthetic polymers dispersed or distributed in an aqueous fluid. The electrical properties of the hydrogel film are dependent upon its moisture content. If the hydrogel possesses appropriate water content, it provides a low impedance electrical path between the electrode's foil layer and a patient's skin. The hydrogel film, however, dries out over time. As a result, its impedance increases over time, thereby undesirably decreasing its effectiveness for signal exchange and energy transfer between a patient and an AED. Once moisture loss has reached a certain level, the hydrogel film, and hence the electrode of which it forms a part, may be unsuitable for use.
A patient's transthoracic impedance typically falls within a range of 25 to 200 Ohms. As electrodes' hydrogel film deteriorate over time, the impedance associated with the electrical path provided by the electrodes may overlap with the typical transthoracic impedance range. Thus, if an AED in a normal operational or “on” state measures an electrode impedance corresponding to a patient's transthoracic impedance, the AED has no inherent way of determining whether partially deteriorated electrodes are currently mounted upon their release liner, or properly functioning electrodes are connected to the patient.
Prior release liners that facilitate electrical testing of electrodes mounted thereupon have typically been unnecessarily complex, expensive to manufacture, unacceptable relative to difficulty of electrode removal, and/or limited relative to the extent to which they permit accurate characterization of an electrode's hydrogel film. A need exists for electrodes and/or release liners that overcome the aforementioned deficiencies.